Multilayer thin film multijunction integrated micropotentiometers

Abstract

Multilayer, thin film multijunction integrated micropotentiometers are formed in an integral multifilm membrane form over a through opening in a nonmagnetic, dielectric substrate. Through the use of conventional photolithographic and etching techniques, integrated structures are formed to include either single elongate heater elements, bifilar heater elements, or trifilar heater elements with multiple return paths. Multijunction thermopiles and resistors are formed with the heater. The individual layers of silicon oxide or silicon nitride, are formed with conventional chemical vapor deposition, sputtering and other known techniques.

What is claimed is: 
     
       1. An integrated micropotentiometer, comprising: a substrate formed of a predetermined thickness of a dielectric material, having a front surface and a rear surface with a through aperture of predetermined shape and size formed therebetween;   a first layer of SiO 2 , formed on the front surface of the substrate to extend over the through aperture in the substrate;   a first layer of Si 3  N 4 , formed on the first layer of SiO 2 , to also extend over the through aperture in the substrate;   a second layer of SiO 2 , formed on the first layer of Si 3  N 4  so as to also extend over the through aperture in the substrate and to provide a mounting surface;   a layer of an electrically resistive material provided on the mounting surface to form a thin elongate heater element having two longitudinal parallel sides and first and second ends, the heater element being shaped and sized to be entirely contained within a periphery of the through aperture in the substrate as defined at the front surface of the substrate in the lateral direction and to extend beyond the periphery of the aperture in the longitudinal direction;   a plurality of first serially-connected thin-film thermocouples, formed and disposed to have their respective cold junctions over the substrate and outside of said periphery of the through aperture and their respective hot junctions arrayed side-by-side overlying the through aperture;   a plurality of serially-connected second thin-film thermocouples, formed and disposed to have their respective cold junctions over the substrate and outside of the periphery of the through aperture on an opposite side thereof with respect to the hot junctions of the first thermocouples, with the respective hot junctions of the second thermocouples overlying the through aperture;   a plurality of resistor elements coupled in series at one end of said heater element, each said resister element having an electrical pad so that said micropotentiometer provides a plurality of output voltages; and,   at least one current return path arranged parallel to said heater element.   
     
     
       2. The integrated micropotentiometer according to claim 1, wherein said pluralities of first and second serially-connected thermocouples are symmetrically disposed on either side of said heater element. 
     
     
       3. The integrated micropotentiometer according to claim 1, wherein said first layer or SiO 2  is formed in compressive stress, said first layer of Si 3  N 4  is formed in tensile stress and said second layer of SiO 2  is formed in compressive stress so that said stresses are balanced to result in a net stress close to zero in value. 
     
     
       4. The integrated micropotentiometer according to claim 3, further comprising: a second layer of Si 3  N 4  formed on the rear surface of the substrate so as to entirely surround a periphery of the through aperture at the rear surface of the substrate.   
     
     
       5. The integrated micropotentiometer according to claim 1, wherein the Thompson effect is reduced by uniform position of said first and second serially connected thin-film thermocouples. 
     
     
       6. The integrated micropotentiometer according to claim 3, further comprising a plurality of current return paths. 
     
     
       7. The integrated micropotentiometer according to claim 3 wherein at least one said current return path is arranged outside of said pluralities of said first and second serially-connected thermocouples. 
     
     
       8. The integrated micropotentiometer according to claim 3, further comprising two symmetrically disposed current return paths between said pluralities of said first and second serially-connected thermocouples constituting a trifilar micropotentiometer. 
     
     
       9. The integrated micropotentiometer according to claim 3, further comprising: first low impedance electrical pads respectively connected to the first and second ends of the heater element and to said return path to enable provision of a controlled electrical current to the heater element; and   second electrical pads connected to extreme ends of each of said pluralities of first and second serially-connected thin-thermal couples to enable electrical connection thereof to an external circuit, wherein said heater element has a length of 20 μm to 800 μm, a width of 1 μm to 1200 μm and a length to width ratio of 4 to 800, and said first electrical pads have an area of 50×50 μm 2  to 400×400 μm 2 .   
     
     
       10. The integrated micropotentiometer according to claim 5, further comprising guard thermocouples arranged on both sides of and in alignment with said pluralities of said first and second serially-connected thermocouples, said guard thermocouples having electrical pads separate from those of said first and second pluralities of thermocouples. 
     
     
       11. The integrated micropotentiometer according to claim 1, wherein the material of said substrate is selected from a group including silicon, ceramic, silicon dioxide, silicon nitride, polyamide and similar materials. 
     
     
       12. The integrated micropotentiometer according to claim 1, wherein said pluralities of said first and second serially-connected thermocouples and heater element are arranged to have a cumulative thermal time constant between 5 msec. and 300 msec. 
     
     
       13. The integrated micropotentiometer according to claim 5, wherein an output of 10-200 mv is contained at said electrical pads connected to said pluralities of said first and second serially-connected thermocouples. 
     
     
       14. The integrated micropotentiometer according to claim 5, further comprising at least one additional layer of SiO 2  formed over said pluralities of said first and second serially-connected thermocouples, said heater element and said output resistors. 
     
     
       15. The integrated micropotentiometer according to claim 3, further comprising: first low impedance electrical pads respectively connected to the first and second ends of the heater element and to said return path to enable provision of a controlled electrical current to the heater element; and   second electrical pads connected to extreme ends of each of said pluralities of first and second serially-connected thin-film thermocouples to enable electrical connection thereof to an external circuit, wherein said heater element has a length of 20 μm to 8000 μm, a width of 20 μm to 6000 μm and a length to width ratio of 0.1 to 10.   
     
     
       16. The integrated micropotentiometer according to claim 1 wherein said heater element is selected from a group including Evanohm™, nickel-chromium alloys and similar materials with small Thompson effect and low temperature coefficients of resistance. 
     
     
       17. The integrated micropotentiometer of claim 14 further comprising a plurality of openings in said additional layer of SiO 2 . 
     
     
       18. The integrated micropotentiometer according to claim 3, further comprising a mounting substrate for holding said substrate, and wiring between said heater element, said output resistors said cold junctions of said first and second thin-film thermocouples and external devices. 
     
     
       19. The integrated micropotentiometer according to claim 1, further comprising: a ceramic lid arranged over said first and second pluralities of serially-connected thin-film thermocouples, said heater element, said output resistors, said wiring and said mounting substrate.   
     
     
       20. The integrated micropotentiometer according to claim 1, wherein said heater element comprises two longitudinally arranged resistive elements connected to the output resistor at a first end and connected to separate electrical pads at a second end forming a bifilar structure. 
     
     
       21. The integrated micropotentiometer according to claim 18, wherein the material of said mounting substrate is selected from a group including ceramic, silicon, glass, and metal. 
     
     
       22. The integrated micropotentiometer according to claim 1, wherein said pluralities of first and second serially-connected thermocouples are asymmetrically disposed on either side of said heater element. 
     
     
       23. The integrated micropotentiometer according to claim 1, wherein said first layer of SiO 2  has a thickness of 20-700 nm, said layer of Si 3  N 4  has a thickness of 20-700 nm, and said second layer of SiO 2  has a thickness of 20-700 nm. 
     
     
       24. The integrated micropotentiometer according to claim 1, further comprising a metal housing enclosing said micropotentiometer wherein said metal housing constitutes at least a portion of said return path.